U.S. patent application number 10/717055 was filed with the patent office on 2004-11-25 for reconfigurable add/drop module.
Invention is credited to Hwang, Seong-Taek, Kim, Sung-Tae, Kim, Young-Seok.
Application Number | 20040234266 10/717055 |
Document ID | / |
Family ID | 33448180 |
Filed Date | 2004-11-25 |
United States Patent
Application |
20040234266 |
Kind Code |
A1 |
Kim, Sung-Tae ; et
al. |
November 25, 2004 |
Reconfigurable add/drop module
Abstract
An add/drop module is disclosed including a first circulator
having first through third ports that are connected to an external
optical fiber, the first circulator outputting an optical signal,
input to the first port, to the second portand outputting an
optical signal, input to the second port, to the third port, an
optical multiplexer/demultiplexer having a multiplexing port
connected to the second port of the first circulator, and adapted
to provide a passage for the optical signal, and a plurality of
demultiplexing ports respectively adapted to provide passages for
demultiplexed channels associated therewith, and a plurality of
add/drop units. Each add/drop unit includes a second circulator
having first through third ports, a second port thereof being
connected to an associated one of the demultiplexing ports, and an
optical switch having first through fourth ports. The first port
being connected to the third port of the second circulator, and at
the third port to the first port of the second circulator, the
first port of the optical switch being selectively connected with
or the third port of the optical switch to establish a path for a
channel to be passed or with the fourth port of the optical switch
to establish a path for a channel to be dropped, the second port of
the optical switch being selectively connected with the third port
of the optical switch to establish a path for a channel to be
added.
Inventors: |
Kim, Sung-Tae; (Kyonggi-do,
KR) ; Hwang, Seong-Taek; (Pyongtaek-shi, KR) ;
Kim, Young-Seok; (Songnam-shi, KR) |
Correspondence
Address: |
CHA & REITER, LLC
210 ROUTE 4 EAST STE 103
PARAMUS
NJ
07652
US
|
Family ID: |
33448180 |
Appl. No.: |
10/717055 |
Filed: |
November 19, 2003 |
Current U.S.
Class: |
398/83 |
Current CPC
Class: |
H04J 14/0212 20130101;
H04J 14/0216 20130101 |
Class at
Publication: |
398/083 |
International
Class: |
H04J 014/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 20, 2003 |
KR |
2003-32059 |
Claims
What is claimed is:
1. An add/drop module connected to an optical signal for
transmitting a multiplexed optical signal in a wavelength division
multiplexing optical transmission system, and adapted to add drop a
channel for the optical signal, comprising: a first circulator
having first through third ports that are both connected to an
optical fiber, the first circulator outputting an optical signal,
input to the first port, to the second port, and outputting an
optical signal, input to the second port, to the third port; an
optical multiplexer/demultiplexer having a multiplexing port
connected to the second port of the first circulator, and adapted
to provide a passage for the optical signal, and a plurality of
demultiplexing ports respectively adapted to provide passages for
demultiplexed channels of the optical signal; and a plurality of
add/drop units each including a second circulator having first
through third ports, a second port of the second circulator being
connected to an associated one of the demultiplexing ports, the
second circulator outputting a channel, input to the second port,
to the third port and outputting a channel, input to the first
port, to the second port, and an optical switch having first
through fourth ports while being connected at the first port to the
third port of the second circulator, and at the third port to the
first port of the second circulator, the first port of the optical
switch being selectively connected either the third port of the
optical switch to establish a path for a channel to be passed or
the fourth port of the optical switch to establish a path for a
channel to be dropped, the second port of the optical switch being
selectively connected with the third port of the optical switch to
establish a path for a channel to be added.
2. The add/drop module according to claim 1, wherein the optical
multiplexer/demultiplexer comprises a waveguide grating router.
3. An add/drop module for a wavelength division multiplexing
optical transmission system, comprising: a first circulator having
a plurality of ports, the first circulator being connected to an
optical fiber; an optical multiplexer/demultiplexer connected to
the first; and at least two add/drop units each including a second
circulator having a plurality of ports, at least one port being
connected to a demultiplexing port of the optical
multiplexer/demultiplexer, and an optical switch having a plurality
of ports, two ports being connected to respective ports of the
second circulator, another port of the optical switch being
selectively connectable to either establish a path for a channel to
be passed or to establish a path for a channel to be dropped.
4. The add/drop module according to claim 3, wherein the add/drop
unit also include a further port of the optical switch that is
selectively connectable to establish a path for a channel to be
added.
5. The add/drop module according to claim 3, wherein the optical
multiplexer/demultiplexer comprises a waveguide grating router.
6. The add/drop module according to claim 3, wherein the first
circulator includes first through third ports that are both
connected to the optical fiber, the first circulator outputting an
optical signal, input to the first port, to the second port, and
outputting an optical signal, input to the second port, to the
third port.
7. The add/drop module according to claim 3, wherein the optical
multiplexer/demultiplexer includes a multiplexing port connected to
the second port of the first circulator, and adapted to provide a
passage for the optical signal, and a plurality of demultiplexing
ports respectively adapted to provide passages for demultiplexed
channels of the optical signal.
8. The add/drop module according to claim 6, wherein the second
circulator includes first through third ports, a second port of the
second circulator being connected to an associated one of the
demultiplexing ports, the second circulator outputting a channel,
input to the second port, to the third port and outputting a
channel, input to the first port, to the second port.
9. An add/drop unit for an add/drop module for a wavelength
division multiplexing optical transmission system, the add/drop
unit comprising: a circulator having a plurality of ports, at least
one port being connectable to a demultiplexing port of an optical
multiplexer/demultiplexer, and an optical switch having a plurality
of ports, two ports being connected to respective ports of the
second circulator, another port of the optical switch being
selectively connectable to either establish a path for a channel to
be passed or to establish a path for a channel to be dropped.
10. The add/drop module according to claim 9, wherein the add/drop
unit also include a further port of the optical switch that is
selectively connectable to establish a path for a channel to be
added.
11. The add/drop module according to claim 10, wherein the
circulator includes first through third ports, a second port of the
second circulator being connected to the demultiplexing port, the
second circulator outputting a channel, input to the second port,
to the third port and outputting a channel, input to the first
port, to the second port.
Description
CLAIM OF PRIORITY
[0001] This application claims priority to an application entitled
"RECONFIGURABLE ADD/DROP MODULE," filed in the Korean Intellectual
Property Office on May 20, 2003 and assigned Ser. No. 2003-32059,
the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a wavelength division
multiplexing (WDM) optical transmission system, and more
particularly to a channel add/drop module for a multiplexed optical
signal advancing in the WDM optical transmission system.
[0004] 2. Description of the Related Art
[0005] Conventional metro WDM optical transmission systems have
been developed that are capable of adding/dropping an optical
signal at each node. Research has been also been conducted into
single-fiber bi-directional ring networks. In the architecture of
such an optical transmission system, add/drop modules perform a
highly important function. Various add/drop modules have been
developed to meet various network architectures. For example, a
reflection type reconfigurable add/drop module using a single
optical multiplexer/demultiplexer has been developed. Typically,
this add/drop module consists of circulators, optical switches, and
fiber Bragg gratings.
[0006] Circulators, used in such an add/drop module, each have a
plurality of ports. In the following description and drawings, one
circulator is designated by a reference numeral "###", its m-th
port is designated by "m" so that a reference numeral "###m" means
the m-th port of the ### circulator.
[0007] FIG. 1 is a diagram illustrating the configuration of a
conventional reconfigurable add/drop module. As shown in FIG. 1,
the add/drop module designated by the reference numeral 100
includes a first circulator 120, that is, CIR1, an optical
multiplexer/demultiplexer 130, that is, WGR, and first through n-th
add/drop units 140 to 150.
[0008] The first circulator 120 has first through third ports 1201
to 1203. The first circulator 120 is connected at its first and
third ports 1201 and 1203 to an external optical fiber 110. The
first circulator 120 outputs to its second port 1202 an optical
signal input to its first port 1201 via the external optical fiber
110, while outputting to its third port 1203 an optical signal
input to its second port 1202 via the optical fiber 110. The first
circulator 120 is a wavelength-independent element, so that it
operates to output an optical signal, inputted to a higher-order
port thereof, to a lower-order port thereof arranged adjacent to
the higher-order port.
[0009] The optical multiplexer/demultiplexer 130 is provided at one
side with one multiplexing port 131(MP) and at the other side with
a plurality of first through n-th demultiplexing ports 132 to
133(DP1 to DPn). The optical multiplexer/demultiplexer 130
demultiplexes a multiplexed optical signal input to the
multiplexing port 131, by units of wavelength, and outputs the
resultant demultiplexed channels to the first through n-th
demultiplexing ports 132 to 133, respectively. The optical
multiplexer/demultiplexer 130 also multiplexes first through n-th
channels .lambda.1 to .lambda.n, input to respective first through
n-th demultiplexing ports 132 to 133 and outputs the resultant
multiplexed optical signal to the multiplexing port 131. The
multiplexing port 131 is connected to the second port 1202 of the
first circulator 120. The optical multiplexer/demultiplexer 130 is
also connected at its first through n-th demultiplexing ports 132
to 133 to respective first through n-th add/drop units 140 to
150.
[0010] The first through n-th add/drop units 140 to 150 include
1.times.2 optical switches 141 to 151(SW1 to SWn), fiber Bragg
gratings 142 to 152, (FBG1 to FBGn), and circulators 143 to 153
(CIR21 to CIR2n), respectively. The first through n-th add/drop
units 140 to 150 have the same configuration. Accordingly, the
following description will be given only in conjunction with the
first add/drop unit 140.
[0011] The SW1 141 is provided at one side with a first port 1411,
and at the other side with second and third ports 1412 and 1413.
The SW1141 is connected at its first port 1411 to the first
demultiplexing port 132, at its second port 1412 to the FBG1 142,
and at its third port 1413 to the CER21 143. The first port 1411 of
the SW1 141 is selectively connected with the second port 1412 or
the third port 1413. The first and second ports 1411 and 1412 of
the SW1 141 are connected in a bar state of the SW1 141, whereas
the first and third ports 1411 and 1413 are connected in a cross
state of the SW1 141.
[0012] The FBG1 142 reflects the first channel .lambda.1
corresponding to a predetermined wavelength.
[0013] The CIR21 143 has first through ports 1431 to 1433. The
CIR21 143 is connected at its second port 1432 to the third port
1413 of the SW1 141. The CIR21 143 outputs the first channel
.lambda.1, input to its second port 1432, to its third port 1433,
thereby dropping the first channel .lambda.1. The CIR21 143 also
outputs another first channel .lambda.1, input to its first port
1431, to its second port 1432, thereby adding the first channel
.lambda.1. The CIR21 143 is a wavelength-independent element, so
that it operates to output an optical signal, input to a
higher-order port thereof, to a lower-order port thereof arranged
adjacent to the higher-order port.
[0014] Now, operation of the add/drop module 100 will be described
in conjunction with a first procedure of passing an optical signal
consisting of first through n-th channels .lambda.1 to .lambda.n
while being input thereto via the external optical fiber 110, and a
second procedure of dropping the first channel .lambda.1 from the
input optical signal, and then adding a new first channel .lambda.1
to the optical signal.
[0015] In the first procedure, the first through n-th optical
switches 141 to 151(SW1 to SWn) are controlled to be in their bar
state by a control unit (not shown). When an optical signal is
input to the first port 1201 of the CIR1 120 in this state, the
CIR1 120 outputs the input optical signal to its second port 1202
to which the optical multiplexer/demultiplexer 130 is connected at
its multiplexing port 131. The optical multiplexer/demultiplexer
130 demultiplexes the optical signal, input to its multiplexing
port 131, in the unit of wavelengths, and outputs the resultant
demultiplexed channels to its first through n-th ports 132 to 133,
respectively. The SW1 141 of the first add/drop unit 140 receives
the first channel .lambda.1 from the optical
multiplexer/demultiplexer 130 at its first port 1411, and then
outputs the received first channel .lambda.1 to its second port
1412 to which the FBG1 142 is connected. The FBG1 142 reflects the
first channel .lambda.1 which is, in turn, re-input to the second
port 1412 of the SW1 141. The SW1 141 then outputs the first
channel .lambda.1 to its first port 1411. The second to n-th
add/drop units operate in the same manner as the first add/drop
unit 140. In this way, the first to n-th add/drop units 140 to 150
pass the first to n-th channels .lambda.1 to .lambda.n input
thereto. The optical multiplexer/demultiplexer 130 receives the
first through n-th channels .lambda.1 to .lambda.n from the first
through n-th add/drop units at its first through n-th
demultiplexing ports 132 to 133, multiplexes the first through n-th
channels .lambda.1 to .lambda.n, and outputs the resultant
multiplexed optical signal to its multiplexing port 131 connected
to the second port of the first circulator 120. The first
circulator 120 then outputs the multiplexed optical signal, input
to its second port 1202, to its third port 1203 connected to the
external optical fiber 110.
[0016] In the second procedure, the control unit controls the SW1
141 to be maintained in its cross state while controlling the
remaining optical switches to be maintained in their bar state.
When an optical signal is input to the first port 1201 of the CIR1
120 in this state, the CIR1 120 outputs the input optical signal to
its second port 1202. The optical multiplexer/demultiplexer 130
demultiplexes the optical signal, input to its multiplexing port
131, in the unit of wavelengths, and outputs the resultant
demultiplexed channels to its first through n-th ports 132 to 133,
respectively. The SW1 141 receives the first channel .lambda.1 from
the optical multiplexer/demultiplexer 130 via first port 1411, and
then outputs the received first channel .lambda.1 to its third port
1413 connected to the second port 1432 of the CIR21 143. The CIR21
143 outputs the first channel .lambda.1, input to its second port
1432, to its third port 1433, thereby dropping the first channel
.lambda.1. The CIR21 143 receives a first channel .lambda.1 at its
first port 1431, and outputs the first channel .lambda.1 to its
second port 1432. In this way, the CIR21 143 adds the first channel
.lambda.1. The SW1 141 receives the first channel .lambda.1 at its
third port 1413, and outputs the received first channel .lambda.1
to its first port 1411. The remaining add/drop units pass the
second to n-th channels B2 to .lambda.n input thereto,
respectively. The optical multiplexer/demultiplexer 130 then
receives the first through n-th channels .lambda.1 to .lambda.n
from the first through n-th add/drop units at its first through
n-th demultiplexing ports 132 to 133, multiplexes the first through
n-th channels .lambda.1 to .lambda.n, and outputs the resultant
multiplexed optical signal to its multiplexing port 131 connected
to the second port of the first circulator 120. The first
circulator 120 then outputs the multiplexed optical signal, input
to its second port 1202, to its third port 1203 connected to the
external optical fiber 110.
[0017] The above mentioned add/drop module 100 is reconfigurable
because respective switching operations of the first through n-th
optical switches for first through n-th channels .lambda.1 to
.lambda.n can be varied.
[0018] However, each add/drop unit of the conventional add/drop
module 100 should be provided with a fiber Bragg grating (or a
reflecting element such as a mirror) in order to pass an associated
channel. It is also necessary to appropriately set the reflection
wavelength of the fiber Bragg grating to meet the wavelength of the
associated channel. Since such a fiber Bragg grating is expensive,
the manufacturing cost of the add/drop module 100 increases
correspondingly. Due to use of such a fiber Bragg grating, the
add/drop module also has a complex configuration.
SUMMARY OF THE INVENTION
[0019] One object of the invention is to provide cost effective
add/drop module. Another object of the present invention is to
provide an add/drop module having a simplified configuration, as
compared to the conventional modules discussed above.
[0020] One embodiment of the present invention is directed to an
add/drop module including a first circulator having first through
third ports that are connected to an external optical fiber. The
first circulator outputs an optical signal, input to the first
port, to the second port, while outputting an optical signal, input
to the second port, to the third port. The module also includes an
optical multiplexer/demultiplexer having a multiplexing port
connected to the second port of the first circulator, and adapted
to provide a passage for the optical signal, and a plurality of
demultiplexing ports respectively adapted to provide passages for
demultiplexed channels associated therewith, and a plurality of
add/drop units. Each add/drop unit includes a second circulator
having first through third ports that are connected at the second
port thereof to an associated one of the demultiplexing ports, the
second circulator outputs a channel, input to the second port, to
the third port while outputting a channel, input to the first port,
to the second port, and an optical switch having first through
fourth ports that are connected at the first port to the third port
of the second circulator, and at the third port to the first port
of the second circulator, the first port of the optical switch
being selectively connected with or the third port of the optical
switch to establish a path for a channel to be passed or with the
fourth port of the optical switch to establish a path for a channel
to be dropped, the second port of the optical switch being
selectively connected with the third port of the optical switch to
establish a path for a channel to be added.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The above objects and advantages of the present invention
will become more apparent by describing in detail preferred
embodiments thereof with reference to the attached drawings in
which:
[0022] FIG. 1 is a diagram illustrating the configuration of a
conventional reconfigurable add/drop module; and
[0023] FIG. 2 is a diagram illustrating the configuration of a
reconfigurable add/drop module according to the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] Now, preferred embodiments of the present invention will be
described in detail with reference to the drawings. In the
following description, a detailed description of known functions
and configurations incorporated herein will be omitted when it may
obscure the subject matter of the present invention.
[0025] One embodiment of the present invention provides a
reconfigurable add/drop module using circulators, and optical
switches. Each of the circulators and optical switches has a
plurality of ports. In the following description, one circulator or
optical switch is designated by a reference numeral "###", its m-th
port is designated by "m" so that so that a reference numeral
"###m" (e.g., 1115) means the m-th port of the ## circulator or
optical switch.
[0026] FIG. 2 is a diagram illustrating the configuration of a
reconfigurable add/drop module according to one embodiment of the
present invention. As shown in FIG. 2, a reconfigurable add/drop
module 200 includes a first circulator 220(CIRl), an optical
multiplexer/demultiplex- er 230 (WGR) and first through n-th
add/drop units 240 to 250.
[0027] The first circulator 220 has first through third ports 2201
to 2203. The first circulator 220 is connected at its first and
third ports 2201 and 2203 to an external optical fiber 210. The
first circulator 220 outputs to its second port 2202 an optical
signal input to its first port 2201 via the external optical fiber
210. The first circulator 220 also outputs to its third port 2203
an optical signal input to its second port 2202 via the optical
fiber 210. The first circulator 220 is a wavelength-independent
element, so that it operates to output an optical signal, input to
a higher-order port thereof, to a lower-order port thereof arranged
adjacent to the higher-order port.
[0028] The optical multiplexer/demultiplexer 230 is provided at one
side with one multiplexing port 231 (MP) and at the other side with
a plurality of first through n-th demultiplexing ports 232 to 233
(DP1 to DPn). The optical multiplexer/demultiplexer 230
demultiplexes a multiplexed optical signal, input to the
multiplexing port 231, in units of wavelength, and outputs the
resultant demultiplexed channels to the first through n-th
demultiplexing ports 232 to 233, respectively. The optical
multiplexer/demultiplexer 230 also multiplexes first through n-th
channels .lambda.1 to .lambda.n, input to respective first through
n-th demultiplexing ports 232 to 233, and outputs the resultant
multiplexed optical signal to the multiplexing port 231. The
multiplexing port 231 of the optical multiplexer/demultiplexer 230
is connected to the second port 2202 of the first circulator 220.
The optical multiplexer/demultiplexer 230 is also connected at its
first through n-th demultiplexing ports 232 to 233 to respective
first through n-th add/drop units 240 to 250. The optical
multiplexer/demultiplexer 230 may include a 1.times.n waveguide
grating router (WGR) integrated on a semiconductor substrate.
[0029] The first through n-th add/drop units 240 to 250 include
circulators 241 to 251 (CR21 to CIR2n) and 2.times.2 optical
switches 242 to 252 (SW1 to SWn), respectively. The first through
n-th add/drop units 240 to 250 have the same configuration. In view
of this, the following description will be given only in
conjunction with the first add/drop unit 240.
[0030] The first add/drop unit 240 includes the CIR21 241 and the
SW1 242.
[0031] The CIR21 241 has first through ports 2411 to 2413. The
CIR21 241 is connected at its second port 2412 to the first
demultiplexing port 232, DP1, of the optical
multiplexer/demultiplexer 230. The CIR21 241 outputs the first
channel .lambda.1, input to its second port 2412, to its third port
2413, and outputs another first channel .lambda.1, input to its
first port 2411, to its second port 2412. The CIR21 241 is a
wavelength-independent element, so that it operates to output an
optical signal, input to a higher-order port thereof, to a
lower-order port thereof arranged adjacent to the higher-order
port.
[0032] The SW1 242 is provided at one side with first and second
ports 2421 and 2422, and at the other side with third and fourth
ports 2423 and 2424. The SW1 242 is connected at its first port
2421 to the third port 2413 of the CIR21 241, and at its third port
to the first port 2411 of the CIR21 241. The first port 2421 of the
SW1 242 is selectively connected with the third port 2423 to
establish a channel passing path or with fourth port 2424 to
establish a channel dropping path. When the SW1 242 is in its bar
state, its first and third ports 2421 and 2423 are connected to
each other, and its second and fourth ports 2422 and 2424 are
connected to each other. On the other hand, when the SW1 242 is in
its cross state, its first and fourth ports are connected to each
other, and its second and third ports 2422 and 2423 are connected
to each other.
[0033] Now, operation of the add/drop module 200 will be described
in conjunction with a first/procedure of passing an optical signal
consisting of first through n-th channels .lambda.1 to .lambda.n
while being input thereto via the external optical fiber 210, and a
second procedure of dropping the first channel .lambda.1 from the
input optical signal, and then adding a new first channel .lambda.1
to the optical signal.
[0034] In the first procedure, the first through n-th optical
switches 242 to 252 (SW1 to SWn) are controlled to be in their bar
state by a control unit (not shown). When an optical signal is
input to the first port 2201 of the CIR1 220 in this state, the
CIR1 220 outputs the input optical signal to its second port 2202
to which the optical multiplexer/demultiplexer 230 is connected at
its multiplexing port 231. The optical multiplexer/demultiplexer
230 demultiplexes the optical signal, input to its multiplexing
port 231, in units of wavelength, and outputs the resultant
demultiplexed channels to its first through n-th ports 232 to 233,
respectively. The CIR21 241 receives the first channel .lambda.1
from the optical multiplexer/demultiplexer 230 at its second port
2422, and then outputs the received first channel .lambda.1 to its
third port 2423 to which the SW1 242 is connected at its first port
2421. The SW1 242 outputs the first channel .lambda.1, input to its
first port 2421, to its third port 2423 connected to the first port
2411 of the CIR21 241. The CIR21 241 then outputs the first channel
.lambda.1, input to its first port 2411, to its second port 2412.
The second to n-th add/drop units operate in the same manner as the
first add/drop unit 240. In this way, the first to n-th add/drop
units 240 to 250 pass the first to n-th channels .lambda.1 to
.lambda.n input thereto.
[0035] The optical multiplexer/demultiplexer 230 receives the first
through n-th channels ), to .lambda.n from the first through n-th
add/drop units at its first through n-th demultiplexing ports 232
to 233, multiplexes the first through n-th channels .lambda.1 to
.lambda.n, and outputs the resultant multiplexed optical signal to
its multiplexing port 231 connected to the second port 2202 of the
first circulator 220. The first circulator 220 then outputs the
multiplexed optical signal, input to its second port 2202, to its
third port 2203 connected to the external optical fiber 210.
[0036] In the second procedure, the control unit controls the SW1
242 to be maintained in its cross state while controlling the
remaining optical switches to be maintained in their bar state.
When an optical signal is input to the first port 2201 of the CIR1
220 in this state, the CIR1 220 outputs the input optical signal to
its second port 2202. The optical multiplexer/demultiplexer 230
demultiplexes the optical signal, input to its multiplexing port
231, in units of wavelength, and outputs the resultant
demultiplexed channels to its first through n-th ports 232 to 233,
respectively. The CIR21 241 of the first add/drop unit 240 receives
the first channel .lambda.1 from the optical
multiplexer/demultiplexer 230 at its second port 2422, and then
outputs the received first channel .lambda.1 to its third port 2423
to which the SW1 242 is connected at its first port 2421. The SW1
242 outputs the first channel .lambda.1, input to its first port
2421, to its fourth port 2424, thereby dropping the first channel
.lambda.1. The CIR21 241 then receives a first channel .lambda.1 at
its second port 2422, and outputs the received first channel
.lambda.1 to its third port 2423. In this way, the CIR21 241 adds
of the first channel .lambda.1. The CIR21 241 receives the first
channel .lambda.1 from the SW1 242 at its first port 2411, and
outputs the received first channel .lambda.1 to its second port
2422. On the other hand, the remaining add/drop units pass the
second to n-th channels .lambda.2 to .lambda.n input thereto,
respectively.
[0037] The optical multiplexer/demultiplexer 230 receives the first
through n-th channels .lambda.1 to .lambda.n from the first through
n-th add/drop units 240 to 250 at its first through n-th
demultiplexing ports 232 to 233, multiplexes the first through n-th
channels .lambda.1 to ?n, and outputs the resultant multiplexed
optical signal to its multiplexing port 231 connected to the second
port 2202 of the first circulator 220. The first circulator 220
then outputs the multiplexed optical signal, inputted to its second
port 2202, to its third port 2203 connected to the external optical
fiber 210.
[0038] As apparent from the above description, embodiments of the
present invention provide a reconfigurable add/drop module in which
add/drop units are configured using circulators and optical
switches without the need for any reflectors. Such aspects of the
present invention a low for reconfigurable add/drop module that has
a simple and cost-effective configuration, as compared to
conventional modules.
[0039] While this invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not
limited to the disclosed embodiment, but, on the contrary, it is
intended to cover various modifications within the spirit and scope
of the appended claims.
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